<?php
/**
 * Prpcrypt class
 *
 * 提供接收和推送给公众平台消息的加解密接口.
 *
 * @author 		gaoming13 <gaoming13@yeah.net>
 * @link 		https://github.com/gaoming13/wechat-php-sdk
 * @link 		http://me.diary8.com/
 */

namespace Gaoming13\WechatPhpSdk\Utils;

class Prpcrypt
{
	public $key;

	function __construct($k) {
		$this->key = base64_decode($k . "=");
	}

	/**
	 * 对明文进行加密
	 * @param string $text 需要加密的明文
	 * @return string 加密后的密文
	 */
	public function encrypt($text, $appid)
	{

		try {
			//获得16位随机字符串，填充到明文之前
			$random = $this->getRandomStr();
			$text = $random . pack("N", strlen($text)) . $text . $appid;
			$iv = substr($this->key, 0, 16);
			//使用自定义的填充方式对明文进行补位填充
			$pkc_encoder = new Pkcs7Encoder;
			$text = $pkc_encoder->encode($text);
            // 尝试使用openssl进行解密
			if(extension_loaded('mcrypt')){
                // 网络字节序
                $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
                mcrypt_generic_init($module, $this->key, $iv);
                //加密
                $encrypted = mcrypt_generic($module, $text);
                mcrypt_generic_deinit($module);
                mcrypt_module_close($module);
            }else{
                $encrypted = openssl_encrypt($text, 'AES-256-CBC', $this->key, OPENSSL_RAW_DATA|OPENSSL_ZERO_PADDING, $iv);
            }

			//使用BASE64对加密后的字符串进行编码
			return base64_encode($encrypted);
		} catch (\Exception $e) {
			@error_log('Encrypt AES Error: ' . $e->getMessage(), 0);
			return FALSE;
		}
	}

	/**
	 * 对密文进行解密
	 * @param string $encrypted 需要解密的密文
	 * @return string 解密得到的明文
	 */
	public function decrypt($encrypted, $appid)
    {

		try {
			//使用BASE64对需要解密的字符串进行解码
			$ciphertext_dec = base64_decode($encrypted);
			$iv = substr($this->key, 0, 16);
			if(extension_loaded('mcrypt')){
                $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
                mcrypt_generic_init($module, $this->key, $iv);

                //解密
                $decrypted = mdecrypt_generic($module, $ciphertext_dec);
                mcrypt_generic_deinit($module);
                mcrypt_module_close($module);
            }else{
                $decrypted = openssl_decrypt($ciphertext_dec, 'AES-256-CBC', $this->key, OPENSSL_RAW_DATA|OPENSSL_ZERO_PADDING, $iv);
            }
		} catch (\Exception $e) {
			@error_log('Decrypt AES Error: ' . $e->getMessage(), 0);
			return FALSE;
		}


		try {
			//去除补位字符
			$pkc_encoder = new Pkcs7Encoder;
			$result = $pkc_encoder->decode($decrypted);
			//去除16位随机字符串,网络字节序和AppId
			if (strlen($result) < 16) {
				return "";
			}
			$content = substr($result, 16, strlen($result));
			$len_list = unpack("N", substr($content, 0, 4));
			$xml_len = $len_list[1];
			$xml_content = substr($content, 4, $xml_len);
			$from_appid = substr($content, $xml_len + 4);
		} catch (\Exception $e) {
			@error_log('Illegal Buffer: ' . $e->getMessage(), 0);
			return FALSE;
		}
		if ($from_appid != $appid) {
			@error_log('Validate Appid Error', 0);
			return FALSE;
		}
		return $xml_content;
	}


	/**
	 * 随机生成16位字符串
	 * @return string 生成的字符串
	 */
	function getRandomStr()
	{

		$str = "";
		$str_pol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";
		$max = strlen($str_pol) - 1;
		for ($i = 0; $i < 16; $i++) {
			$str .= $str_pol[mt_rand(0, $max)];
		}
		return $str;
	}
}